Pulse echo object locator



P. K. CHATTERJEA ETAL PULSE ECHO OBJECT LOCATOR Filed June 28, 19465 F/ G H n 3/ l Al'llll RELAY Y n.6 I 9 (o vanua-TER lu/TER CLI/PER l nu sul r TER JQ *T- le 6 Rice/VER I3 DEMODULAR 4J- l F G 2 OUTPUT WAVE A g 0F l OCILLTOR 7\ aum/r wave 0F CILLATOR l Arm? /Nvsns/ow ,Q D "l Off fw l/vPur WAVE ro cup/5R /o/ l l i E d vm/fz/z op Mmmm f, M

o Mm, aurPur uve y by #44d afm 0F cL/PPER lo l ME 2l a Patented Oct. 23, 1951 PULSE ECHO OBJECT LOCATOR Prafulla Kumar Chatterjea and Leslie Wilfred Houghton, London,

England,

assignors, by

mesne assignments, to International Standard Electric Corporation, New York, N. Y., a corporation of Delaware Application June Z8, 1946, Serial No. 680,001 In Great Britain June 8, 1945 Section 1, Public Law 690, August 8, 1946 Patent expires June 8, 1965 9 Claims.

The present invention relates to methods of locating obstacles, such as aircraft, by means of reected electromagnetic waves.

In Fig. of the specification of the co-pending application Serial No. 468,570, led December 10, 1942, now United States Patent No. 2,454,772, issued November 30, 1948, there is illustrated an arrangement for measuring the distance of objects in which the reected pulses are combined with the inverted original pulses in order to obtain unidirectional rectangular pulses whose duration is proportional'to the distance of the object. The rectangular pulses are integrated by means of a direct current instrument which then indicates the distance of the object.

The purpose of the present invention is to provide a convenient stabilising circuit for the arrangement by means of which the indicating instrument is caused to give a steady zero reading until an object comes within the range of Y the locating arrangement, when it suddenly operates to indicate the distance, and its reading follows the object while it remains within range.

The invention provides an arrangement for locating obstacles comprising means including a saw-tooth relaxation oscillator for generating an original train of regularly repeated electric pulses, means for radiating the said pulses, means for receiving the pulses after reflection from an obstacle, means for applying the received pulses to synchronise a second saw-tooth relaxation oscillator, means for deriving jointly from the said oscillators a train of unidirectional pulses having a characteristic depending upon the distance of the obstacle, means for indicating the saidcharacteristic, and means for applying the original train of pulses to synchronise the second oscillator in the absence of any reected pulses.

The invention will'be described with reference to the accompanying drawing in which:

j numeral I generates waves having a period T, which are applied to synchronise a pulse generator 2 of conventional type which delivers short pulses at equal intervals T to the radio transmitter 3 and transmitting aerial 4. The pulses reected from the object are picked up on the V-`receiving aerial l5 andare demodulated in the receiver 6 and applied to synchronise a second saw-tooth relaxation oscillator represented generally by the numeral l, which is similar to I,

vand should be adjusted to generate waves of period slightly greater than T when running freely. An amplifying valve 8 is provided to lnvert the saw-tooth waves generated by I. The output waves from the oscillator 'I and from the valve 8 are then mixed in a common load resistance 9.

Referring now to Fig. 2, a curve a shows the wave voltage generated by the oscillator I after inversion in the valve 8, plotted against time. The waves at the output of the oscillator I shown at b, Fig. 2, are synchronsed by the reected pulses obtained from the receiver 6, and will be displaced with respect to the waves a by the'time interval t between the original and reflected pulses, where t is the time taken for the pulses to travel from the aerial 4 to the obstacle and back to the receiving aerial 5. After the waves a and b have been mixed together in the load resistance 9 they will appear in the form of rectangular pulses of duration t as shown shaded at c in Fig. 2. These rectangular pulses. are then applied to a device I0 (Fig. 1) which converts them into unidirectional pulses d (Fig. 2) having duration t and repeated at intervals equal to T. The device I0 may for example be any suitable limiting device which cuts off the lower portions of the waves c.

The unidirectional pulses d are applied to an ordinary direct current voltmeter I I. The reading of the voltmeter will evidently be equal to t.V/T, where V is the voltage corresponding to the height of the unidirectional pulses d, as shown in Fig. 2. Thus since T is known, the voltmeter reading gives t, and hence the distance of the object.

The inverting valve 8 could alternatively have been connected to invert the output of the oscillator I instead of that of oscillator I. The resulting unidirectional pulses d would be of opposite sign, but the operation would be otherwise the same.

The meter Il may clearly be calibrated in terms of the distance of the obstacle, and this calibration Will be independent of the amplitude of the reected pulses. In case the amplitude of the saw-tooth waves should not be maintained sufliciently constant, the calibration would be affected, but this can be overcome by the device I0 which can be arranged in well known fashion as an amplitude limiter so that the unidirectional pulses d are'of lixed amplitude. The measurement then depends only on the duration of the ing pulses are supplied from the pulse generator v v2 (Fig. 1) to the oscillator 'i through a synlchronising amplifying valve I2.

into the same phase so that :te-:0. There are then no pulses d and the instru-ment l'l .reads zero. The valve l2 is controlled byabias 'voltage derived from the receiver 6 over the conductor 13. As soon as any reflectedpulses are received,

a bias voltage sufficient to cut off the valve 112,

is developed in the receiver 6 by an arrangement of known type (not shown) such 2as LthatJcorrl'- monly used for generating an automatic `rgain control voltage for an amplifier. In this '-Waythe local synchronising control is removed, and the reflected .pulses take over the synchronisng of fthe oscillator 11 in the manner already explained. JThis means that` aval-ue f t slightly `less than `T vvill be obtained as soon as the .object cornes Within range, and 'the instrument `l"| Willsuddenlyg'ive practically its maximum reading. "As the object moves about, so the instrument will continuously indicate the -distance according .to the value df t. It Will be evident thatjif desired, a relay I4 could be .connected in parallel with "the vltineter I'I to 'the'output of the device I0 having contacts (not shown) "for 'operating 'an 'alarm for "the purpose `of calling `the attention of an operatoras Ysoon 'as 'an object cor-nes With- 'in range.

Y The details of the circuit ofEig.'1`will now'oe described. 'A high 'tens'ion source for 'the valves is vv'inl'fended to lbe .connected to lthe terminals '.15 lpositive') I and T6 (negative and earthed).

' 4The vtwo oscillator circuits! and'lare vexactly similar and will .be described together. 'Ifhey .consist .of grid-contrlled vgas-'filled valves .(l'l

and lil), ythe anodes ef which are 4supplied with supplied by pai-rsof '.resistances (21,."22 an'dZB, '211) connected to vthe high tension .terminals i5 and ld-the cathodes beingconnected to the junction .points .of .the respective -pairs .of .rsistances Condensers 25 and 25 are the cathode Aicy-.pass condensers. The control ,grids lare earthed through thefusual .resistancesl and "28.

lThe saw-tooth waves are -.generated in the `oscillators l and .l vby .the periodic .cliarginglof condensers 2Q and 39, through resistances 5l 9. and T20, and their periodic-discharging through fthe valves E l and I3 in the WelLknownmanner. 'fResistances 3l and 32 are provided lforl'lirnitinglthe discharge currents in order to prevent damage to ythe valves.

`The anode of the invertingvalve I8 issupplied with current from'terminal .f 5 'through the resistance '33. The cathode islbiassedby'means of aV conventional condenser-resistance n'etvvork"34, and 35 is the usual grid resistance. .'*Ihe lvltage variations of the oondenser29 are 'communicated -to the control grid through the blocking .condenser 36. `The inverted saw-.tooth Waves Aare .supplied .to the .load .resistance .'9 ".from. .the .anode offthe valve A8 through .thelb'locling condenserfl :and stopping. resistance $3.

.The synchronizing valve HL2 has..elements 39 -and All 'corresponding tothe relements 33 andfll 'This 'will have the effect of bringing the Wave's'fa andb (fFig. 21),-

in the receiver 6 over conductor 3, instead of to earth. A corresponding by-pass condenser 42 is provided.

The loc'alsy-nchronisingpulses for :the pulse generator 2 are applied to the control grid Vof .the valve l2 through a blocking condenser V"I3, and the output pulses are applied to the control l 'grid'of the "oscillator valve I8 through a blocking il condenser "Mand vstopping resistance 45. .10 meilectedpulseszfrom the receiver Ei are also ap- The plied 'to thi's'feon-trol grid over the stopping resistan'cek 416; Finally, the voltage variations of "the condenser i3?) are applied to the load resist- .ance 18 @through `the blocking condenser 4l. and

1.5 stopping resistance 48Vto be mixedwith the inverted Waves from the valve 8.

`vitfhasalre'a-iy"been stated that the waves from the oscillator 'l could have been inverted instead ori-those from the oscillator l. In this case all 2o that is necessary is tov interchange the connecf vdenser`.'--'.2`1la`nd730; Y

It xvill be evident .that the Ylcca'l syncliron'is'ing .pulSesObtainedrOm the generator 22 andlsup- .tions ci. .the -condensei's Sfand M to the non- 25 y:plied:tothe valve `lf2sqhouldbe innega'tivesense 3o of'thegeneratorWherethepulses are negative,

cr by supplying .an .additional inverting valve notshownl... .'.The reflectedfsynchronising ,pulses -app'lied `over resistance d'5 must, ofcoursalikewise. bearrangedtobeinpositivefsense.

35 vThe loadlresistance '9 gprovidesfthesimnlest possible .mixing .ldevice' for l.combining `the waves a and b-dffigfZ Variousother arrangements are .clearly .-possible; Vfor .example .two `mixing -valves Knot shown) vs'haringa,commonloaztreinsistance could .be connected.. respectively .'to .the

output ycircuit .off-valves J8 Yand vI8, -oralternatively miii-ngcouldbe done a.multiple Agrid valve. fSuch larrangem'entsare Wellsknownlito 1.thoselskilled.inthearltV 7 45 QWhatis claimed is:

f 1l :An-.arrangementfor loca-tinge obstaclesv` com- .'-pi sing rneans-i-ncludinga saw-tooth relaxation oscillator .-for generating lfan l.original `train-,of

regularly :repeated electric pulses, means-for.

50 .radiating the -said ,-pulses, means lfor Y.rl-eceiv-ing 75 l.ant.combmation ,Wave :inisuchfsmanner {asftolobs -.combining the=sawtooth Wave outputs ,of .said

.'rst.. and -second oscillators, `means. for Iindicating Ithe original trani-offpulses-to synchronise the second oscillator: in thefabsence tiffany. relieeted pulses. g

I- 2. .An arrangement fortlocatingobstaclesgzcomo5 prising means including a sawgtoot-h :relaxation --osoillator rfor .generating 7an origina-1 I tr-.ain of regularly vrepeated electric pulses, `Ineansfor .radiating .thesaidf pulses, means .for receiving .the pulses after reilection from -.an..obstacle, .means 70 4{for} applyingftheareceived .pulses -tosynchronise a ..second :saw-.tooth :relaxation oscillator, ,means .for .inverting the waves from ronepf, said .oscilf-lators,.means.-fer .combining the savlftootli Waves ,of said .oscillators-means ,to translate thejresultthe said characteristic, -Aandimea-ns fior. applying tain unidirectional rectangular pulses of duration proportional to the distance of the obstacle, means lfor applying the said pulses to an indicating instrument, and means for applying the original train of pulses to synchronise the second oscillator in the absence of any reiiected pulses.

3. An arrangement according to claim 2 comprising means controlled by the incoming reflected pulses for preventing the said original train of pulses from synchronising the second oscillator.

4. An arrangement according to claim 3 comprising means for giving an alarm signal When reflected pulses commence to be received by the said arrangement.

5. An arrangement according to claim 1 in which an amplifying valve is provided by means of which the said original train of pulses is applied to synchronise the said second oscillator and in which means is provided for blocking the 8. An arrangement according' to claim '7 comprising an alarm relay connected in parallel with the said voltmeter.

9. An arrangement for locating obstacles comprising means including a saw-tooth relaxation oscillator for generating an original train of regularly repeated electric pulses, means for radiating said pulses, means for receiving the pulses after reflection from an obstacle, a second saw-tooth relaxation oscillator, means for applying the received pulses to synchronise said second oscillator, means for inverting the waves from one of said oscillators, means for combining the saw-tooth Waves of said oscillators, and means to translate the resultant combination Wave to obtain unidirectional rectangular pulses of duration proportional to the distance of the obstacle.

PRAFULLA KUMAR CHA'I'IERJEA. LESLIE WILFRED HOUGHTON.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,250,708 Hers July 29, 1941 2,391,411 Goble Dec. 25, 1945 2,416,333 Lehmann Feb. 25, 1947 2,428,427 Loughren Oct. 7, 1947 2,428,799 Hayes Oct. 14, 1947 

